November 17, 1911] 



SCIENCE 



691 



earth, horse manure, etc., invariably died with- 

 out showing any indication of further devel- 

 opment. 



Further observations on Habronema muscw 

 were made during the summer of 1911, when 

 it was found commonly present in house flies 

 in Colorado and Nebraska. A series of stages 

 in the development of the parasite was ob- 

 tained by examination of various stages of the 

 fly from larva to imago, and it became evident 

 that the fly acquires its infection during its 

 larval stage. This suggested the hypothesis 

 that Hahronema muscce is the larval stage of a 

 nematode parasitic during its adult stage in 

 the horse, inasmuch as horse manure is a 

 favorite breeding place of the house fly. The 

 structure of the esophagus of Hahronema 

 muscce suggested the further hypothesis that 

 this parasite belonged either to 8piroptera 

 megastom,a or to S. microstom,a, nematodes 

 which occur in the stomach of the horse. 



Ordinarily the testing of the hypothesis that 

 Hahronema muscce is the larval stage of a 

 horse parasite would require properly con- 

 trolled feeding experiments, but, in September 

 of the present year, the problem of the identity 

 of the parasite was solved in another way. 

 The stomachs of two horses were examined 

 shortly after death. In one of them, a few 

 adult nematodes were found which, from their 

 naked eye appearance, closely resembled Spi- 

 roptera microstoma. In the other, a large 

 number of the same species of adult worms 

 was found, apd in addition numerous smaller 

 nematodes of various sizes. Microscopical ex- 

 amination of the worms collected from these 

 horses revealed the presence of a complete 

 series of stages in the development and growth 

 of a single species of nematode from larva to 

 adult, only the one species being represented, 

 except that a few individuals of a species of 

 Trichostrongylus were also present. The 

 smallest forms corresponded perfectly to the 

 nematodes found in adult flies, and the cor- 

 rectness of the hypothesis that Hahronema 

 muscce is the larval stage of a nematode para- 

 sitic during its adult stage in the horse, was 

 thus confirmed. The adults of Hahronema 

 muscce, though very similar to, proved to be 



different from, Spiropiera microstoma, most 

 noticeably in the structural details of the head 

 and pharynx, vagina of the female and bursa 

 and spicules of the male. The spicules alone 

 present sufiieient evidence of a specific differ- 

 ence in the two forms, as will appear from the 

 following measurements : 



In Hahronema muscce the left spicule meas- 

 ures about 2.5 mm. in length and about 5 ^ in 

 diameter near its middle, the right spicule 

 about 500 fi in length by about 10 /j. in diam- 

 eter near its middle. In Spiropiera micros- 

 toma, or, giving this species its correct generic 

 designation, in Hahronema microstoma the 

 left spicule measures about 800 fn in length by 

 about 15 /J, in diameter near its middle, the 

 right spicule about 350 /j. in length by about 

 20 fjL in diameter near its middle. 



The life history of Hahronema muscce, as 

 determined by the results of the investigations 

 which have been briefly sketched in the present 

 paper, may be summed up as follows : 



A horse infested with the adult worms ex- 

 cretes their embryos in its feces. These em- 

 bryos enter the bodies of fly larvae developing 

 in the feces from eggs deposited by house flies. 

 During the development of the fly larvas and 

 pupse, the worms with which they have become 

 infested also undergo a process of growth and 

 development, reaching their final larval stage 

 at about the time the flies emerge from the 

 pupal state. Further development of the 

 worms waits upon the swallowing of the in- 

 fested flies by a horse, in which event the life 

 cycle becomes completed by the growth of the 

 worms to maturity. 



Of interest to entomologists and sanitarians 

 is the fact that Hahronema muscce affords a 

 means of determining with some degree of 

 accuracy what proportion of the flies occur- 

 ring in a given locality find their breeding 

 place in horse manure, to this extent, that if 

 examination of a considerable number of flies 

 shows that a certain per cent, are infected, it 

 may be safely assumed that at least that per- 

 centage of the flies in the locality have devel- 

 oped in horse manure. A percentage obtained 

 in this way would of course probably be con- 

 siderably smaller that the actual percentage, as 



